This application is a U.S. National Phase Application of PCT International Application PCT/JP99/04897.
1. Field of the Invention
The present invention relates to an angular rate sensor.
2. Background of the Invention
As a known angular rate sensor of the prior art, there is disclosed one in page 26 through page 33 of the Journal of Nippondenso Engineering Society (Vol. 38, No. 3, 1994). This angular rate sensor comprises an exciting unit for providing a tuning fork vibrator with vibration, a means for detecting a vibration level of the vibrator, a detection means for detecting Coriolis"" force generated responsive to an angular rate, a first amplifier for amplifying an output signal of the means for detecting vibration level, a rectifier circuit for rectifying an output signal of the first amplifier to obtain a DC voltage, a comparator of an output voltage of the rectifier circuit with a reference voltage, and a variable gain amplifier connected to the exciting unit in a manner that a vibrating amplitude of the tuning fork vibrator is controlled to be constant by varying an amplification factor for amplifying a voltage, which is produced by shifting phase of an output voltage of the first amplifier by 90 degrees according to an output voltage of the comparator.
The prior art technique described above has not been sufficient to ensure reliability of the angular rate sensor, as it is difficult to make a detection when there is an open circuit in a connecting line between a detecting electrode and a detection circuit, a change in sensitivity due to deterioration of the detecting electrode, or a breakdown developed in the detection circuit.
An angular rate sensor includes an exciting unit for providing a vibrator with vibration a means for detecting a vibration level of the vibrator, a first detection means for detecting Coriolis"" force generated responsive to an angular rate, a second detection means for detecting a signal of a reverse polarity to that of the first detection means, a driving circuit for taking as an input a signal from the means for detecting vibration level and outputting a signal to the exciting unit, and a first detection circuit and at second detection circuit wherein detected signals are being input respectively from the first detection means and the second detection means. A structure as described above is able to realize the angular rate sensor having a function of detecting even a change in sensitivity due to a breakdown and deterioration, with remarkably improved reliability.